Frequency Stability Research Articles

Reserve Technique in Integrating Large Sustainable Energy Sources: A Case Study of the Tunisian Grid

The increasing integration of sustainable energy sources, such as wind and solar power, into the national electricity grid presents significant challenges in terms of frequency control and grid stability. Additionally, the imbalance between electricity supply and demand introduces dynamic frequency variations. However, according to the literature, the impact of high penetration of renewable energy sources on the Tunisian grid has not been extensively analyzed using power system simulator for engineering (PSS/E). This research paper explores how the primary reserve technique participates to maintain frequency within acceptable ranges in the Tunisian electrical grid. Individual generators contribute to the total power output, thereby influencing frequency deviation. The primary frequency control action by each generator is proportional to its frequency deviation and inversely proportional to its governing drop, which measures the generator’s sensitivity to frequency changes. This paper analyzes frequency stability in the Tunisian grid under scenarios with and without different rates of sustainable energy source penetration, which barely reached 3.5% in 2023. In Tunisia, the use of sustainable energy is essential not only for ensuring grid stability but for combating climate change and reducing carbon emissions, aligning with the country’s environmental goals. The transition to sustainable energy significantly reduces the carbon footprint of the power sector, offering a sustainable solution for mitigating the adverse effects of climate change. Dynamic simulations were conducted for the isolated Tunisian system, separate from the interconnected grid, focusing on the critical scenario of the loss of a large electricity production unit. This study also examined the absence of sustainable energy integration and the effects of integration of different rates of renewable energy to evaluate the impact of reserves on the continuity of the Tunisian electrical service. Simulation results, which considered a 2023 grid model, show that with an integration trial of 20% renewable energy and, in the worst-case scenario, which represents the loss of the largest production group in the grid, the primary reserve of a given group—defined by the quantity of active energy—can be rapidly deployed to restore the balance between electricity supply and demand. Thus, reserves are a crucial solution for maintaining frequency within reasonable limits and ensuring the continuity of electrical services in Tunisia with varying rates from 10% to 20% integration of different sustainable energy sources.

Broad Microbial Community Functions in a Conventional Activated Sludge System Exhibit Temporal Stability.

Wastewater microbial communities within conventional activated sludge (CAS) systems can perform hundreds of biotransformations whose relative importance, frequency, and temporal stability remain largely unexplored. To improve our understanding of biotransformations in CAS systems, we collected 24 h composite samples from the influent and effluent of a CAS system over 14 days, analyzed samples using high-resolution mass spectrometry (HRMS), and conducted a nontarget analysis of our HRMS acquisitions. We found that over 50% of the chemical features in the influent were completely removed, and the daily number of detected features exhibited low variability with a coefficient of variation of 0.07. Additionally, we found 352 Core chemical features present in every sample at both locations. We used chemical features to search for evidence of 19 potential biotransformations and detected 9 of these biotransformations at a frequency of over 80 times per day, where evidence for dehydrogenations, hydroxylations, and acetylations was most frequently detected. The daily number of detections for the 9 biotransformations exhibited coefficients of variation ranging from 0.13-0.20, revealing the broad temporal stability for these wastewater microbial community functions. This stability contrasts with the previously observed temporal variability for micropollutant biotransformations, suggesting that micropollutant biotransformations are linked to specialized microbial community functions.

Simulation of Voltage and Frequency Stabilization in PV-Based Microgrids Using Virtual Synchronous Generator Control

In recent years, distributed generation technologies and micro-grids have garnered increasing attention, particularly with the rapid growth of renewable energy sources (RESs) integrated via power electronic converters. As the penetration of RESs in modern power systems rises, voltage and frequency support, traditionally provided by synchronous generators, can be effectively managed by Virtual Synchronous Generator (VSG) control. This paper presents the modeling and analysis of voltage and frequency stability enhancement in a PV-based micro-grid system using VSG control. The micro-grid system under study operates at 400V, 50Hz, and is integrated with a 0.4kV power distribution line. Mathematical models of the VSG control strategy are developed in MATLAB/Simulink. Simulation results demonstrate that VSG control significantly improves the voltage and frequency stability of the PV-based micro-grid system.

Estimation of Quantitative Inertia Requirement Based on Effective Inertia Using Historical Operation Data of South Korea Power System

In low-inertia systems with a high penetration of renewable energy, the rotational kinetic energy and inertia constant are significant factors in determining frequency stability. The energy released owing to the frequency decrease during contingency represents a portion of the inertia that a synchronous machine possesses in the normal state. However, when securing inertia or planning additional resources to secure frequency stability, inertia in the normal state is analyzed as the standard rather than the amount of energy released during a fault. Therefore, in this paper, we define the actual energy emitted from a synchronous machine as Effective inertia. In order to evaluate Effective inertia in various operating conditions, we conducted a comprehensive review on approximately 24,627 cases from the years 2019, 2020, and 2021. As a result, in systems with low rotational kinetic energy, both low- and high-frequency nadirs were observed, indicating high uncertainty. However, Effective inertia presented a consistent trend regarding the energy release aligned with the minimum frequency. For instance, the rotational kinetic energy required to satisfy the frequency standard was 23 GWs, while the required Effective inertia was 858 MWs. We emphasize that securing inertia based on rotational kinetic energy includes additional imaginary energy that does not contribute to frequency, resulting in an energy requirement greater than that needed for Effective inertia. Therefore, in order to secure the frequency stability of the future system, the actual required energy amount based on Effective inertia will be presented and utilized in the inertia market and FFR (Fast Frequency Response) resource design.

Record-high power, low phase noise synchronously-pumped optical parametric oscillator tunable from 2.7 to 4.7 μm

Within the domain of optical frequency comb systems operating in the mid-infrared region, extensive exploration has been undertaken regarding critical parameters, such as stabilization, coherence, or spectral tunability. Despite this, certain essential parameters remain inadequately addressed, particularly concerning light source stability at high average powers. This study explores stability limitations of an optical parametric oscillator system when scaling to several watts of average power of the idler. Notably, the highest average power reported in the 3–5 μm region, reaching 10.3 W for the idler output at 3.1 μm, is achieved. Additionally, we analyze the phase noise and beam quality of both idler and signal beams and identify the onset of higher order modes as limiting for stability at high-power operation. Finally, we estimate the free-running optical linewidth of our idler beam to be ∼300 kHz, undermining the high passive temporal stability of our source. These findings represent a significant advancement toward the realization of highly stable high-power optical frequency combs in the mid-infrared region, thereby facilitating applications previously constrained by light source average powers and quality limitations.

Improvement in the Sagnac-loop laser frequency stabilization

Improvement in the Sagnac-loop laser frequency stabilization

High detectivity terahertz radiation sensing using frequency-noise-optimized nanomechanical resonators

We achieve high detectivity terahertz radiation sensing using a silicon nitride nanomechanical resonator functionalized with a metasurface absorber. High performances are achieved by striking a balance between the frequency stability of the resonator and its responsivity to absorbed radiation. Using this approach, we demonstrate a detectivity D*≈3.4×109cm⋅Hz/W and a noise equivalent power NEP≈36pW/Hz that outperform the best room-temperature on-chip THz detectors, such as pyroelectric detectors, while maintaining a comparable thermal response time of ≈200 ms. Our optical absorber consists of a 1-mm diameter metasurface, which currently enables a 0.5–3 THz detection range but can easily be scaled to other frequencies in the THz and infrared ranges. In addition to demonstrating high-performance terahertz radiation sensing, our work unveils an important fundamental trade-off between frequency stability and responsivity in thermal-based nanomechanical radiation sensors.

Phase demodulation method for stable long-haul frequency transmission based on the Michelson interferometer.

In this Letter, we present a fiber-optic radio frequency (RF) transmission scheme based on phase modulation with an interferometric detection structure. A self-developed Michelson interferometer (MI) is used to demodulate the frequency signal via an electrically controlled optical shifter. The two complementary outputs from the interferometer are detected using a balanced detector, which suppresses the common-mode noise of the fiber link. The structure is tested in the laboratory using a frequency transfer system over a 560 km fiber link. Experimental results show that a stable 2.4 GHz frequency transmission with a fractional frequency instability of 3.9 × 10-14 at 1 s and 6.2 × 10-17 at 10,000 s is achieved. Compared with the frequency transmission system based on intensity modulation and direct detection, the frequency instability is improved from 7.3 × 10-14 to 3.9 × 10-14 at 1 s. We believe that the proposed method will be useful for the construction of time-frequency synchronous fiber networks.

Copy number variants underlie major selective sweeps in insecticide resistance genes in Anopheles arabiensis.

To keep ahead of the evolution of resistance to insecticides in mosquitoes, national malaria control programmes must make use of a range of insecticides, both old and new, while monitoring resistance mechanisms. The outdoor-biting malaria vector Anopheles arabiensis is of increasing concern for malaria transmission because it is apparently less susceptible to many indoor control interventions, yet knowledge of its mechanisms of resistance remains limited. Furthermore, comparatively little is known in general about resistance to non-pyrethroid insecticides such as pirimiphos-methyl (PM), which are crucial for effective control in the context of globally high resistance to pyrethroids. We performed a genome-wide association study to determine the molecular mechanisms of resistance to the pyrethroid deltamethrin (commonly used in bednets) and PM (widespread use for indoor spraying), in An. arabiensis from 2 regions in Tanzania. Genomic regions of positive selection in these populations were largely driven by copy number variants (CNVs) in gene families involved in metabolic resistance. We found evidence of a new gene cluster involved in resistance to PM, identifying a strong selective sweep tied to a CNV in the carboxylesterase genes Coeae2g - Coeae6g. Using complementary data from another malaria vector, An. coluzzii, in Ghana, we show that copy number at this locus is significantly associated with PM resistance. Similarly, for deltamethrin, resistance was strongly associated with a novel CNV allele in the Cyp6aa / Cyp6p cluster (Cyp6aap_Dup33). Against this background of metabolic resistance, resistance caused by mutations in the insecticide target sites was very rare or absent. Mutations in the pyrethroid target site Vgsc were at very low frequency in Tanzania, yet combining these samples with 3 An. arabiensis individuals from West Africa revealed a startling evolutionary diversity, with up to 5 independent origins of Vgsc-995 mutations found within just 8 haplotypes. Thus, despite having been first recorded over 10 years ago, Vgsc resistance mutations in Tanzanian An. arabiensis have remained at stable low frequencies. Overall, our results provide a new copy number marker for monitoring resistance to PM in malaria mosquitoes, and reveal the complex picture of resistance patterns in An. arabiensis.

Analysis and Control of Frequency Stability in Low-Inertia Power Systems: A Review

Analysis and Control of Frequency Stability in Low-Inertia Power Systems: A Review

An oven controlled piezoelectric MEMS dual-resonator platform with frequency stability of [formula omitted]100 ppb over industrial temperature range

This work demonstrates a piezoelectric MEMS dual-resonator platform with an oven control. The platform includes a micro-oven in-chip, which integrates a frequency output resonator and a temperature sensing resonator. The two resonators operate using a phase-locked loop system, one in width-extensional (WE) mode and the other in width-shear (WS) mode. An equivalent thermal model of the dual-resonator platform is established and both resonators exhibit extremely uniform temperature distributions. The real-time temperature of the resonators is monitored by measuring the frequency difference between the two resonators and a closed-loop oven control is implemented to maintain the dual-resonator platform at an oven-set temperature. The reported oven controlled piezoelectric MEMS dual-resonator platform exhibits a measured frequency stability of ±100 ppb across the industrial temperature range of −40 to 85 °C. This result signifies the promising potential of the device in high-end timing applications.

Research on miniaturized frequency steering system based on atomic clock

In order to generate a high-performance RF signal, by analyzing the traditional frequency steering system, and aiming at the goal of miniaturization and engineering, this paper designs a miniaturized frequency steering system based on dual-atomic clock. In addition, we have carried out research on key technologies such as high-precision frequency deviation measurement and precision frequency regulation. On this basis, a frequency deviation measurement and correction system is designed. And according to the theoretical analysis, the measuring accuracy of the frequency deviation measurement approach can reach 1.0 × 10-14, besides, the step frequency tuning can also reach 1.125 × 10-14. What's more, some related experiments, the RF signal synthesized from a Rb clock and a master has an accuracy of 2.26 × 10-13, and also the frequency stability of 104 s in terms of the Allan deviation reaches 2.36 × 10-14, suggesting that the overall performance of the rubidium atomic clock has been greatly improved.

Temperature and Frequency-Dependent Dielectric Properties Prediction of Oxide Glasses by Machine Learning

The dielectric properties of oxide glasses are essential for telecommunications, where thermal and frequency stability of devices are crucial. However, predicting the temperature and frequency-dependent dielectric properties of glasses is complex using empirical models and computational methods. To address this challenge, machine learning (ML) models with descriptor sets in two different domains—the chemical composition domain and the element physical and chemical properties domain—were employed to predict the dielectric constant and loss of oxide glasses, along with their temperature and frequency dependencies. Additionally, Shapley additive explanations (SHAP) analysis was conducted to interpret the hidden relationships among the data. Compared to experimental values, the ML models perform well in terms of root mean square error (RMSE) and the coefficient of determination (R2). Moreover, the ML models using element physical and chemical properties descriptors demonstrate the potential to predict the dielectric properties of glasses with unknown components.

Comprehensive Control Analysis of Dual DC-DC Output Converter for Integration of Offshore Wind Turbine Systems

This paper presents an in-depth exploration of control state-space modeling tailored for high-power isolated dual output DC-DC (ISO-D2) converter, with a particular emphasis on elucidating system dynamics through the derivation of state-space matrices and transfer functions. Employing state-of-the-art analysis techniques, this study offers a systematic framework for comprehending the converter's behavior across varied operational scenarios. Through the derivation of state-space matrices encompassing state, input, and output parameters, the converter's dynamic response is encapsulated in a precise mathematical representation. Additionally, transfer functions are established to facilitate frequency domain analysis and stability evaluation. These derived models furnish invaluable insights into the performance characteristics of the converter, thus enabling the formulation of robust control strategies. Particularly, the derived state-space matrices and transfer functions serve as instrumental tools for the design of advanced control algorithms, crucial for optimizing the performance of high-power isolated dual output DC-DC (ISO-D2) converters, in real-world applications such as solar plants and offshore DC wind farms.

High-stability adaptive frequency comparison method based on fuzzy area characteristics

To meet the high-accuracy requirement of time and frequency measurement and its synchronization in complex environment, a high- stability adaptive frequency comparison method based on fuzzy area characteristics is proposed in this paper. First, the frequency of the measured signal is measured by using FPGA and pulse-filling frequency measurement technology to obtain the frequency coarse value of the measured signal. Second, a communication protocol between FPGA (Field Programmable Gate Array) and DDS (Direct Digital Synthesizer) is established to enable DDS to recognize the information from FPGA. Third, the frequency coarse value of the measured signal is sent to FPGA and converted into the corresponding “frequency word” by DDS. Finally, according to the communication protocol between FPGA and DDS, an adaptive frequency standard signal with the same frequency coarse value as the measured signal is generated by controlling the DDS with the “frequency word”. Then there is a small relative frequency deviation between the frequency of the measured signal and the frequency of the adaptive frequency standard signal. The experiment results show that the frequency stability based on the proposed method can reach 1.76 × 10-13 /s, and the accuracy of the frequency synchronization is better than 5 Hz.

Electrogastrography in Adult Gastroparesis: A Systematic Review and Meta-Analysis.

Gastroparesis is a delay in gastric emptying without mechanical obstruction, lacking a clear pathophysiological mechanism, but with multiple histological abnormalities including loss of interstitial cells of Cajal, which may alter slow waves. We can assess slow waves with electrogastrography. To determine the prevalence and range of abnormalities in gastric slow waves in adults with gastroparesis using electrogastrography. We systematically searched Medline, Embase, LILACS, Web of Science, and Cochrane Register of Controlled Trials. We included studies with patients older than 18years with gastroparesis, assessed using electrogastrography. We evaluated the percentage of duration of the recording in which the dominant power was in normogastria, tachygastria, and bradygastria; dominant frequency; power ratio; change in post-stimulus dominant power; and dominant frequency instability coefficient. Methodological quality was assessed using the Joanna Briggs Institute tool. Data were synthesized using narrative summary and meta-analysis. A total of 3730 articles were reviewed, including 31 articles with 1545 patients and 340 controls. Compared to controls, gastroparetics patients had less normogastria (fasting: 50.3% versus 65.8%) (post-stimulus: 54.3% versus 66.5%), more bradygastria (fasting: 37.7% versus 13%) (post-stimulus: 31.9% versus 16.3%), and more tachygastria (fasting: 16.1% versus 4.6%) (post-stimulus: 18.3% versus 5.2%). Gastroparetics had less change in post-stimulus dominant power (1.45dB versus 5.03dB) and less power ratio (1.4 versus 5.26). Gastroparetic patients present abnormalities in the frequency and changes in the post-stimulus power of slow waves, possibly secondary to a reduced number of interstitial cells of Cajal, as described in these patients.

Clonal hematopoiesis impacts frailty in newly diagnosed multiple myeloma patients: a retrospective multicenter analysis

Somatic mutations of hematopoietic cells in the peripheral blood of normal individuals refer to clonal hematopoiesis of indeterminate potential (CHIP), which is associated with a 0.5–1% risk of progression to hematological malignancies and cardiovascular diseases. CHIP has also been reported in Multiple Myeloma (MM) patients, but its biological relevance remains to be elucidated. In this study, high-depth targeted sequencing of peripheral blood from 76 NDMM patients revealed CHIP in 46% of them, with a variant allele frequency (VAF) ranging from ~ 1 to 34%. The most frequently mutated gene was DNMT3A, followed by TET2. More aggressive disease features were observed among CHIP carriers, who also exhibited higher proportion of high-risk stages (ISS and R-ISS 3) compared to controls. Longitudinal analyses at diagnosis and during follow-up showed a slight increase of VAFs (p = 0.058) for epigenetic (DNMT3A, TET2, and ASXL1) and DNA repair genes (TP53; p = 0.0123). A more stable frequency was observed among other genes, suggesting different temporal dynamics of CH clones. Adverse clinical outcomes, in term of overall and progression-free survivals, were observed in CHIP carriers. These patients also exhibited weakened immune T-cells and enhanced frailty, predicting greater toxicity and consequently shorter event-free survival. Finally, correlation analysis identified platelets count as biomarker for higher VAF among CHIP carriers, regardless of the specific variant. Overall, our study highlights specific biological and clinical features, paving the way for the development of tailored strategies for MM patients carrying CHIP.

Design and Analysis of Miller Compensated Two-Stage Operational Amplifier

Abstract. With the development of integrated circuit technology, the size of electronic equipment continues to reduce, and speed continues to increase. Operational amplifiers are the key circuit in analog ICs, and the required performance of operational amplifiers is also increasingly high, research and design of high-performance operational amplifiers has become one of the key topics of today's research. A CMOS two-stage operational amplifier with high unity-gain bandwidth is analysed and designed with an appropriate Miller-compensation technique in this research to improve the frequency characteristics and stability. The design is based on 180nm CMOS process. Its performance is simulated and analysed in Cadence software environment. The performance parameters are shown by simulation results that the amplifier has a gain of 61.81dB, a GB (unity-gain bandwidth) of 907.42MHz and a phase margin of 75.02. The experimental results show that it achieves high unity-gain bandwidth while ensuring gain and stability. Through this study, the principles of two-stage operational amplifiers and their compensation as well as the design and simulation are shown in detail in both theoretical and experimental sections.

Isolated microgrid frequency stabilization through nonlinear model predictive control of a gas engine generator set

Gas engine generator sets are applied in microgrids due to their capability to provide reliable, responsive and efficient distributed power generation, enhancing grid resilience and enabling the integration of renewable energy sources. This article proposes a methodology for stabilizing the frequency of an isolated microgrid subjected to a measurable disturbance by controlling the power of a premixed turbocharged natural gas engine. Control difficulties of this task include strongly nonlinear dynamics, time delay in the air-fuel path and constrained operating conditions. Conventional control methods like proportional-integral control have difficulties solving these problems, and require extensive tuning efforts and gain scheduling to deliver acceptable performance, prompting adoption of advanced control strategies. The presented approach utilizes a cascaded control architecture with a nonlinear model predictive controller (NMPC) for high level control and engine specific low-level controllers for controlling the intake manifold pressure and air-fuel ratio. The NMPC captures the inherent nonlinear dynamics, accounts for an input delay and handles state-dependent constraints. The cascaded control architecture enables the usage of a comparably simple model for the NMPC design, reducing the computational cost and the parametrization effort. This additionally enables application of the high level controller for different gas engine types and allows design of the controller in a simple simulation environment prior to the experiments on the real engine. Experimental results highlight the NMPC’s ability to control the engine at its physical limits over the entire load range without inducing frequency oscillations using just one parameter set. This emphasizes the robustness of the presented approach, making it a promising solution for real-world applications.

Coordinated control strategy for improving frequency security of LCC[sbnd]HVDC sending-end system with large-scale wind power

To improve the frequency security of the LCCHVDC sending-end system with high penetration of wind power system and achieve optimal utilization of frequency regulation resources, a cooperative control strategy involving wind power and LCCHVDC in frequency regulation is proposed. Firstly, under a variety of scenarios, the power support requirements of LCCHVDC sending-end system are analyzed according to the power regulation margin of various frequency regulation resources and the disturbance power, and a multi-time scale frequency regulation control strategy for DFIG based wind farms is proposed, which combines the advantages of variable speed control and variable pitch angel control. And a cooperative control strategy of DFIG and LCCHVDC considering the frequency regulation deadband is proposed. Then, based on the maximum power regulation margin of synchronous generators and wind farms, the key control parameters of relative control links are designed to enable them autonomously adjust the active power according to various scenarios to involve in inertia response and primary frequency regulation task. Finally, the effectiveness of the control strategy is verified by the simulation model of LCCHVDC sending-end system with large-scale wind power, which significantly improves the frequency security and stability.